The invention relates to a payment system in which use is made of electronic payment cards, in particular "chip cards" or "smart cards". Under consideration in the present application are, in particular, payment cards which can be used for paying call costs in public telephone terminals. However, other services and goods can also be paid for in this way. This development is in fact referred to as a so-called "electronic purse". Under consideration in this connection is the payment of generally none too large amounts by means of electronic payment cards on which a balance is previously entered. Payment takes place by reducing the balance on the card. Of course, measures have to be taken in order to arrange for the balance reduction to benefit the supplier; systems for this purpose are still being developed and tests are taking place in that field. To place an initial balance on the card and increase the balance later, there must be an infrastructure of terminals and the like if this form of payment is to be accepted. It appears possible to use the public telephone terminals for this purpose. Such terminals act as "charging stations" for the electronic payment cards. Of course, the public telephone terminals remain suitable as means for conducting telephone calls and offering any other telecommunication facilities via the downstream central telephone system or telecommunication system. Payment of such telephone calls and any other facilities may, at the same time, take place by means of the "electronic purse". Although the payment of telephone/telecommunication costs, in particular, is considered below, it is emphasized that the invention, as explained below, is not limited thereto and is equally applicable for payment for other services or goods by means of an "electronic purse". The "charging" of payment cards need not occur via telephone terminals either, but can equally well occur via other terminals, for example, terminals which are now used for issuing cash (so-called "cash points").
After a payment card has been provided with an initial balance, that balance is reduced by the telephone terminal in accordance with a rate for the telephone costs. The provision of an initial balance and the replenishment of the balance after the passing of time can also occur via the telephone terminal. To do this, connection has to be made to a central administration system which, onto the one hand, enters the amount desired by the user on the card and, on the other hand, ensures that the amount can be received, for example, by sending an account to the user or via (after authorization) electronic reduction of the balance of a bank account belonging to the user.
The measures proposed according to the present invention are intended to combat errors and frauds in the processes mentioned (the use/payment process and the "balance process").